It's the most popular sport in the world, and it invokes riotous passion like no other – everywhere but in America, that is.

In America, the game the rest of the world calls "football" is known as "soccer," and as far as popularity goes . . . well, let's just say it's not football.

But not this Saturday, when TV sets across the U.S. will be tuned in to watch the United States play England in the opening round of the World Cup -- a match in South Africa that is expected to generate more North American viewers than any soccer game in history.

It's a game soccer aficionados hope will finally put their sport alongside baseball, football and basketball in the consciousness of American fans.

“It’s a very unique game, because it’s something that U.S. sports fans can get right off the bat,” said Trevor Hayward, the editor of World Soccer Reader. “It’s U.S.-England ... they’ll get that rivalry right away. It’s such a huge opportunity to grow the sport and put the game in front of fans.”

But will the excitement over this game be enough to have a permanent impact, or will most people tune away when it's over, only to return four years later?

“I’m not one who is so convinced,” said Brian Berger, a sports marketing and public relations consultant in Portland, Ore., and the founder of Sports Business Radio. “I think the World Cup shines a spot on soccer. The casual fan who doesn’t watch soccer is going to tune in. But when it’s over, is the casual fan paying attention on a regular basis?”

Most pundits give the U.S. a fighting chance against England, especially after the Americans toppled a powerhouse Spanish team during a run to the finals of the FIFA Confederations Cup in South Africa last summer.

Moreover, the U.S. has shown that it can be competitive in World Cup play, having reached the quarterfinals in 2002 and having earned a draw against eventual champion Italy in group play in 2006. England, meanwhile, is still stinging from its failure even to qualify for the UEFA European Championships in 2008.

“I think the perception of the American team has been good in recent years because they’ve performed in past World Cups very well,” said former English soccer star Steve McManaman, who now serves as a commentator. “[England] knows America has a good team. They have a lot of experience ... I think they’re going to be a threat to England. I think it will be a difficult game for England.”

Soccer supporters say the game will undoubtedly bring more eyeballs to the sport, which they hope will pay dividends over time in the form of higher television ratings and greater attendance at games in the United States.

And the further the U.S. advances, the more Americans will be likely to tune in.

“The game itself will provide a bump,” said Mark Abbott, president of Major League Soccer, the largest professional league in America. “When you look at last year with the Confederations Cup, that was a story that was widely followed in the United States. The game Saturday is likely to be one of the biggest games in terms of media coverage and viewership. It’s just a great opportunity for the sport.”

Soccer has grown substantially in the last 20 years in America, going from a niche sport to one that now features a viable professional league – Major League Soccer (MLS) -- and robust coverage of international matches on television and the Internet. More than 17 million people in North America tuned in to the World Cup final between Italy and France in 2006, and more than 120 million people watched at least one minute of the World Cup tournament.

In the four years since the last World Cup, soccer coverage has increased both on television and online. Networks including Fox Soccer Channel and ESPN have expanded the availability of games from the English Premier League, Italy’s Series A and Spain’s La Liga, while giving strong promotion to the UEFA Champions League, a tournament involving the top European club teams. Meanwhile, top European clubs including Real Madrid, AC Milan and others have attracted sellout crowds during tours to major U.S. cities.

But television coverage of MLS games has been flat, with only a handful of games airing nationally each week. While the league is growing in size -- it will expand from 16 to 19 teams by 2012 -- it has struggled to overcome the perception that it is not as competitive as European leagues.

Soccer's TV ratings and attendance fall well short of the established major sports in America, and sports marketing experts caution that winning a single soccer game -- or even the biggest tournament in the world -- will fix that.

“Let’s say the U.S. won the World Cup,” Berger said. “I’m not convinced that MLS will see a huge increase in their popularity and be on par with the NFL, NBA and Major League Baseball.

"I see the World Cup like the Olympics. It comes around every four years. It has a huge global audience. The casual fan is going to tune in because it’s about heritage and country. But is the casual fan then going to go watch MLS? I don’t think so.”

MLS officials insist they aren’t banking the league’s future on the success or failure of the U.S. team or the World Cup in general. But early indications are that buzz over the tournament and Saturday’s game has helped.

IBISWorld, a research firm, reported this week that average attendance at MLS games is up nearly 11 percent from the same period last year. The company expects attendance will rise more than 15 percent overall for the 2010 season.

“It shouldn’t be a make or break, but one of the biggest obstacles the sport has is just pure exposure,” Hayward said. “This game just offers that, and you have to find a way to capitalize on it some way.”